The use of coated (i.e., sized) glass fibers and their incorporation into various resins for reinforcing purposes is well known. Bare glass fibers are substantially smooth rod-like members having surfaces which are highly hydrophilic in nature and thus will not typically exhibit a bonding relationship with polymeric materials sufficient to provide reinforcement properties thereto. That is, the lack of bonding between the bare glass fibers and the polymeric material causes the glass fibers and the polymeric material to separate from one another and thus are not useful for the manufacture of glass fiber-reinforced products. It is conventional therefore to provide a thin layer of an aqueous size composition to the surfaces of the bare glass fibers which is compatible with and serves to improve the bonding relationship between the glass fibers and the polymeric material. Thus, glass fibers utilized for the reinforcement of resinous polymeric materials conventionally have an aqueous-based size applied to their surface and the fibers are then wound into a package. The packages are dried for the purpose of eliminating moisture after which the fibers can be used for reinforcement purposes, either in continuous lengths or as cut fibers in polymeric resin matrices such as nylon, acetal, polybutyl terephthalate and polypropylene.
Typically, it is necessary to employ a specially-formulated size composition in dependence upon the resin matrix in which the sized glass fibers will be dispersed as reinforcement media. The size formulations are thus specifically formulated so that the sized glass fibers will be compatible with the resin matrix in which they are dispersed. It would therefore save considerable processing expense owing to the requirement for separate formulations in dependence upon the desired resin matrix in which the coated glass fibers will be used, if a universal size formulation could be achieved which is functional in a variety of resin matrices. Moreover, it would be beneficial if a size could be employed which, while requiring no drying, could be directly blended into the resin and molded therewith to provide satisfactory reinforcement. Another important role of a size is to protect the glass fibers against abrasion and provide a strand of the desired integrity so as to avoid unwanted filamentation during handling. This is especially important for chopped glass used for compounding with thermoplastics as filamentized glass may create what is commonly called "fuzz" or "clumps" which, in turn, create problems in feeding to the extruder and in keeping a homogeneous blend. On the other hand, it is often desired that the strand filamentizes easily once it is incorporated into the molten thermoplastic. Complete filamentation results in a uniform dispersion of the glass filaments and in a homogeneous polymer/reinforcing fiber blend. Moreover, undispersed bundles of fibers may create surface or appearance defects in a molded part.
The requirements for a high strand integrity prior to incorporation into a polymer and good glass dispersion in the finished part are opposite in terms of formulation of an aqueous size, so aqueous size formulations are often the result of a compromise to obtain an acceptable balance of integrity and dispersability. It is therefore another purpose of this invention to significantly improve the dispersion of fibers in the polymer in order to obtain a homogeneous blend of polymer/reinforcing fibers and good appearance of the molded part and at the same time maintain or significantly improve the abrasion protection and the integrity of the glass strands before blending into the polymer. The present invention is directed to a solution to these problems.
According to the present invention, there is provided a non-aqueous hot melt coating for glass fibers consisting of a cycloaliphatic epoxy resin, an ethylene-ethyl acetate copolymer, a microcrystalline wax, a phenolic-modified terpene resin, and an organosilane. The invention relates to the discovery that the amino silane coupling agents, which have been observed to gel epoxy resins when combined in hot melts, are surprisingly non-gelling with cycloaliphatic epoxy resins at processing temperatures (i.e., 300.degree.-400.degree. F.) necessary to produce hot melt size compositions. Accordingly, amino-organosilane coupling agents which are typically necessary when formulating a coating for glass fibers can be utilized with cycloaliphatic epoxy resins so that the resulting coating will be compatible with a number of polymeric resins to achieve properties of a molded glass fiber-reinforced product which are comparable to the aqueous sizes specially formulated for the particular polymeric resins.
Further advantages of the present invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follows.